2004A&A...414L..53T

L1521E seems unique among starless cores. It stands out in a distribution of a ratio (R) that we define to asses core evolution, and which compares the emission of the easily-depleted C¹⁸O molecule with that of the hard to deplete, late-time species N₂H⁺. While all cores we have studied so far have R ratio lower than 1, L1521E has an R value of 3.4, which is 8 times the mean of the other cores. To understand this difference, we have modeled the C¹⁸O and N₂H⁺ abundance profiles in L1521E using a density distribution derived from 1.2 mm continuum data. Our model shows that the C¹⁸O emission in this core is consistent with constant abundance, and this makes L1521E the first core with no C¹⁸O depletion. Our model also derives an unusually low N₂H⁺ abundance. These two chemical peculiarities suggest that L1521E has contracted to its present density very recently, and it is therefore an extremely young starless core. Comparing our derived abundances with a chemical model, we estimate a tentative age of ≤1.5x10⁵yr, which is too short for ambipolar diffusion models.